Electroplating

ABSTRACT

NOVEL ACID AQUEOUS ELECTROPLATING BATHS FOR FORMING LUSTROUS ZINC DEPOSITS CONTAINING A WATER-SOLUBLE ZINC SALT, USUAL LUSTERING AGENTS AND WETTING AGENT, OPTIONALLY AN ADDITIONAL CONDUCTING SALT, A THIOUREA DERIVATIVE OF THE FORMULA   R-NH-C(=S)-N(-R1)-R2   WHREIN R IS SELCTED FROM THE GROUP CONSISTING OF ALKYL OF 6 TO 22 CARBON ATOMS, A MONO- OR POLYNUCLEAR ARYL WHICH MAY OPTIONALLY BE SUBSTITUTED WITH AN ALIPHATIC OR AROMATIC GROUP, ARYLALKYL AND CYCLOALKYL, R1 IS SELECTED FROM THE GROUP CONSISTING OF HYDROGEN AND HYDROXYALKYL OF 2 TO 6 CARBON ATOMS WHICH MAY OPTIONALLY BE INTERRUPTED BY AN ETHER OXYGEN AND R2 IS HYDROXYALKYL OF 2 TO 6 CARBON ATOMS WHICH MAY BY OPTIONALLY INTERRUPTED BY AN ETHER OXYGEN, AN AN AROMATIC CARBONYL COMPOUND SELECTED FROM THE GROUP CONSISTING OF   R3-CO-R4 AND R3-A-CO-R4   WHERE R2 IS ARYL SUCH AS PHENYL AND LOWER-ALKYL PHENYL WITH ALKYL OF 1 TO 7 CARBON ATOMS. A IS SELECTED FROM THE GROUP CONSISTING OF SATURATED ALKYLENE WITH 1 TO 7 CARBON ATOMS AND UNSATURATED ALKYLENE WITH 2 TO 7 CARBON ATOMS, AND R4 IS LOWER ALKYL WITH 1 TO 7 CARBON ATOMS OPTIONALLY SUBSTITUTED WITH KETO, CARBOXY, AND CARBALKOXY OF 1 TO 7 CARBON ATOMS, AND TO A NOVEL ELECTROPLATING METHOD OF FORMING IMPROVED LUSTROUS ZINC DEPOSITS WITH GOOD DUCTILITY AND ZINC DEPOSITS FORMED BY SAID METHOD.

3,795,594 ELECTROPLATING Josef Hartenstein, Hilden, and Monika Nee, Dusseldorf- Holthausen, Germany, assignors to Henkel & Cie G.m.b.H., Dusseldorf-Holthausen, Germany N Drawing. Filed Apr. 13, 1972, Ser. No. 243,827 Claims priority, application Germany, Apr. 16, 1971,

P 21 18 512.6 Int. Cl. C23b /12, 5/46 US. Cl. 204--55 R 13 Claims ABSTRACT OF THE DISCLOSURE Novel acid aqueous electroplating baths for forming lustrous zinc deposits containing a water-soluble zinc salt, usual lustering agents and wetting agents, optionally an additional conducting salt, a thiourea derivative of the formula S /R; R-NH-ii-N wherein R is aryl such as phenyl and lower-alkyl phenyl with alkyl of 1 to 7 carbon atoms, A is selected from the group consisting of saturated alkylene with 1 to 7 carbon atoms and unsaturated alkylene with 2 to 7 carbon atoms, and R is lower alkyl with 1 to 7 carbon atoms optionally substituted with keto, carboxy, and carbalkoxy of 1 to 7 carbon atoms, and to a novel electroplating method for forming improved lustrous zinc deposits with good ductility and zinc deposits formed by said method.

STATE OF THE ART Most of the commercial zinc electroplating baths for forming lustrous zinc deposits operate with an alkaline bath and the most widely used alkaline electroplating baths are the cyanide lustrous zinc baths. However, the detoxification of the waste water resulting from these electroplating baths causes an economical problem which results in criticism of these baths and various attempts have been made to-replace cyanide lustrous zinc baths with other types of baths.

These attempts have included cyanide-free alkaline zinc baths and also acid zinc baths in which the waste water can be disposed of without difliculty and without great expense. In spite of the advantage of simple disposal of waste water, the acid zinc baths of the prior art have a number of disadvantages which make them unsuitable for extensive industrial use.

In some baths, the zinc deposits are dull, and when one succeeds in imparting luster to the deposits, their depth dispersion still leaves much to be desired and the current density range in which lustrous deposits are obtained is within very narrow limits. Apart from this, the deposits obtained frequently show a great embrittlement. In spite of all efforts, an effective prevention of all the disadvantages at the same time has not been found and United States Patent O ice only limited and partial improvements have been obtained, which often result in intensifying another disadvantage. Therefore, until now, there has been no acid lustrous zinc bath which provides over a wide range of current densities embrittlement-free deposits of good luster with good depth dispersion.

OBJECTS OF THE INVENTION It is an object of the invention to provide novel aqueous acid electroplating baths for forming lustrous zinc deposits.

It is another object of the invention to provide a novel method of forming lustrous zinc deposits over a wide range of current densities.

These and other objects and advantages of the invention will become obvious from the following detailed description.

THE INVENTION The novel aqueous acid electroplatic baths of the invention contain a water-soluble zinc salt, usual lustering agents and wetting agents, optionally an additional conducting salt, a thiourea derivative of the formula wherein R is selected from the group consisting of alkyl of 6 to 22 carbon atoms, a monoor polynuclear aryl which may optionally be substituted with an aliphatic or aromatic group, arylalkyl and cycloalkyl, R is selected from the group consisting of hydrogen and hydroxyalkyl of 2 to 6 carbon atoms which may optionally be interrupted by an ether oxygen and R is hydroxyalkyl of 2 to 6 carbon atoms which may be optionally interrupted by an ether oxygen, and an aromatic carbonyl compound selected from the group consisting of wherein R is aryl, A is selected from the group consisting of saturated alkylene with 1 to 7 carbon atoms and unsaturated alkylene with 2 to 7 carbon atoms, and R is lower alkyl with 1 to 7 carbon atoms optionally substituted with keto, carboxy, and carbalkoxy of l to 7 carbon atoms.

Preferably, R is alkyl of 6 to 22 carbon atoms, phenyl or naphthyl which may be further substituted with alkyl of 1 to 10 carbon atoms such as methyl or nonyl, halogens such as chlorine or bromine, sulfonyl or phenyl, cycloalkyl of 5 to 12 carbon atoms such as cyclopentyl, cyclohexyl, menthyl or bornyl and phenyl lower alkyl such as benzyl or phenethyl.

R is aryl, preferably phenyl which may be optionally substituted with a lower alkyl of l to 7 carbon atoms. A is a saturated oiunsaturated alkylene of 1 to 7 carbon atoms, preferably 1 to 3 carbon atoms, such as methyl, ethyl, propyl, vinylene, etc. R is preferably a lower alkyl of 1 to 7 carbon atoms, optionally substituted with keto, carboxy, and carbalkoxy of 1 to 7 carbon atoms, such as methyl, methylcarboxy, and methylcarbethoxy.

Examples of suitable aromatic carbonyl compounds are acetophenone, benzoyl-acetic acid, alkyl esters of benzoylacetic acid, such as the ethyl ester, benzoyl-acetone, benzal acetone and a-acetyl naphthalene.

Examples of suitable compounds of Formula I are N-hexyl-N'-(' -hydroxyethoxy)-ethyl-, N-octyl-N'- ('y-hydroxy-ethoxy -propyl', N-dodecyl-N'- ('y-hydroxyethoxy) -ethyl-, N-octadecyl-N-( -hydroxyethoxy) -ethyl-, N-phenyl-N'- 'y-hydroxy-ethoxy -ethyl-, N-diphenyl-N'- ('y-hydroxyethoxy) -propyl-,

N-a-naphthyl-N- y-hydroxyethoxy) -ethyl-, N-to syl-N- ('y-hydroxyethoxy) -propyl-, N-nonylphenyl-N- ('y-hydroxyethoxy) -ethyl-, N-b enzyl-N'- -hydroxyethoxy) -ethyl-, N-cyclopentyl-N'- ('y-hydroxyethoxy) -propyl-, N-cyclohexyl-N'- ('y-hydroxyethoxy) -ethyl-, N-p-menthyl-N'- 'y-hydroxyethoxy -ethyl-, Nbornyl-N'- ('y-hydroxyethoxy) -propyl-, N-phenyl-N -hydroxyethoxy -isopropyl- N-ctyl-N'-' -hydroxyethyl-, and N-benzyl-N'-bis'- ('y-hydroxyethyl) -thiourea.

The thioureas of Formula I can be prepared by known methods by reacting a mustard oil of the formula R-N-CS with an amine of the formula wherein R, R and R have the above definitions or by reacting a thiourea of the formula R-NH--CS--NH with a lower alkylene oxide such as ethylene oxide, propylene oxide or butylene oxide.

The concentration of the thiourea derivatives of Formula I in the zinc electroplating baths may be between 0.01 to 10 gm. per liter, preferably between 0.1 to 5.0 gm. per liter, of bath liquid. The current density used for the electroplating method is between 0.5 to 8 a./dm. at a bath operating temperature of 10 to 40 C. preferably 15 to 30 C. The pH of the acid baths is generally in the range of 3 to 5.

It has now been discovered that the luster of the zinc deposits obtainable with these baths may be appreciably improved while retaining very good ductility if the bath additionally has a content of the aromatic carbonyl compounds described above.

I The concentration of the aromatic carbonyl compounds in the zinc electroplating baths may be between 0.01 to 10 gm. per .liter of bath liquid, preferably between 0.1 to 5 gm. per liter, of bath liquid.

The water-soluble zinc salt may be any of the usual zinc salts such as zinc chloride or zinc sulfate or mixtures thereof. Preferably, the acid baths contain 25 to 450 gm. per liter of bath liquid of the zinc salt. The additional conducting salt which may be present in the bath is preferably a water-soluble aluminum salt such as its chloride or sulfate. The amount of said additional conducting salt is 1 to 50 gm. per liter of bath liquid.

Various wetting agents can be added to the acid baths in amounts of 0.5 to gm. per liter of bath liquid. Especially preferred for use in an acid zinc chloride bath are non-ionic wetting agents by the adducts of an alkylene oxide such as ethylene oxide and/or propylene oxide and high molecular weight aliphatic alcohols or alkyl phenols such as the adducts of 2 to 100 moles of ethylene oxide and 1 mole of a straight or branched chain aliphatic alcohol of 8 to 22 carbon atoms and mixtures thereof or to alkylphenols such as nonylphenol, fatty amines, fatty acid amides or fatty mercaptans. In acid zinc sulfate baths, the wetting agents are preferably anionic compounds such as fatty alcohol sulfates or fatty alcohol ether sulfates, alkyl sulfonates or al kylaryl sulfonates or non-ionic compounds of the polyalkylene glycol type. Examples of suit able additives of these types are sulfates or ether sulfates of fatty alcohols of 8 to 18 carbon atoms and polyethylene glycols and polypropylene glycols with a molecular weight of 200 to 600.

Examples of suitable lustering agents are thiourea,

N-phenyl-N'- -hydroxyethyl) -ethyl-thiourea, N-benzyl-N- ('y-hydroxyethyl) ethyl-thiourea, N-octyl-N'- 'y-hydroxyethoxy propyl-thiourea, N-a-naphthyl-N- -hydroxyethoxy) ethyl-thiourea, N-cyclohexyl-N'- -hydroxyethoxy) -propyl-thiourea, N-benzyl-N'-bisy-hydroxyethyl -thiourea.

Further examples of customary lustering agents for acidic zinc baths include protein, gelatins, protein degradation products, polyimines, and dithiocarbamic acid derivatives.

The preferred wetting agents for acid zinc chloride baths are non-ionic compounds of the type of adducts ethylene oxide and high molecular aliphatic alcohols or alkylphenols, such as adducts of from 2 to mol of ethylene oxide and 1 mol of straight chain or branched chain aliphatic alcohols of 8 to 22 carbon atoms and mixtures thereof, or to nonylphenol.

The best results are obtained in acid zinc sulfate baths when the wetting agents are anionic compounds such as fatty alcohol sulfates or fatty alcohol ether sulfates type such as C -C fatty alcohol sulfates or C -C fatty alcohol ether sulfates or non-ionic compounds of the polyalkylene glycol type, such as polyethyleneand polypropylene glycols having a molecular weight of 200-600.

Particularly favorable results with respect to covering capacity and degree of luster may be obtained in the acid zinc chloride bath with the aromatic carbonyl compounds to be used in the inventions, when the zinc chloride bath contains adducts of ethylene oxide and isononyl alcohol as the wetting agent. The quantity of wetting agent used in the bath is generally0.5-10 g./l. of bath liquid.

In the following examples there are described several preferred embodiments to illustrate the invention. However, it should be understood that the invention is not intended to be limited to the specific embodiments.

EXAMPLE I An aqueous Zinc electroplating bath was prepared with the following composition: gm./liter of crystalline zinc chloride (ZnCl 6H O), 175 gm./ liter of ammonium chloride, 0.5 gm./liter of N-phenyl-N'-(q hydroxyethyl)- ethyl-thiourea and 5 grrL/liter of the adduct of 17 moles of ethylene oxide and 1 mole of isononyl alcohol. The bath had a pH of 4.6. The electroplating bath provided lustrous, ductile zinc deposits with a good covering power at an operating temperature of 15 to 30 C. over a current density range of 2 to 5 a./dm.

EXAMPLE II An aqueous zinc electroplating bath containing 100 gm./liter of crystalline zinc chloride (ZnCl -6H O), 50 gm./ liter of crystalline aluminum chloride (AlCl -6H O), gm./liter of ammonium chloride, 2 gm./liter of N- benzyl-N-('y-hydroxyethyl)ethyl-thiourea and 4 gm./liter of 'the adduct of 20 moles of ethylene oxide and one mole of nonylphenol with a pH of 3 was operated at temperatures of 15 to 30 C. over a current density range of 0.3 to 5.0 a./dm. and provided bright to lustrous ductile Zinc deposits with a good covering power.

EXAMPLE III An aqueous zinc bath containing 400 g./liter of crystalline zinc sulfate (ZnSO -7H O), 15 g./liter of ammonium chloride, 30 g./liter of boric acid, 0.7 g./liter of N-octyl-N- ('y-hydroxyethoxy)-propyl-thiourea and 5 g./ liter of sodium salt of the C C -fatty alcohol sulfate and having a pH of 3.5 was operated at a temperature of 15 to 30 C. over a current density range of 0.5 to 3 a./dm. to obtain bright, ductile zinc coatings with satisfactory covering power.

EXAMPLE IV An aqueous zinc bath containing 240 g./liter of crystalline zinc sulfate (ZnSO -7H O), 30 g./liter of crystalline aluminum sulfate (Al (SO -18H O), l5 g./liter of sodium acetate, 0.2 g./liter of N-a-naphthyl-N'-('y-hydroxyethoxy)-ethyl-thi0urea and 4 g./liter of' sodium salt of the C -C -fatty alcohol sulfate and having a pH of 4.0 was operated at at temperature of 15 to 30 C. over a current density range of 0.5 to 5 a./dm. to provide bright, ductile zinc coatings with excellent covering power.

EXAMPLE v An aqueous zinc bath containing 400 g./liter of crystalline zinc sulfate (ZnSO -7H O), g./ liter of ammonium chloride, 30 g./liter of boric acid, 1 g./liter of N-cyclohexyl-N'-('y-hydroxyethoxy)-propyl-thiourea, 5 g./liter of sodium lauryl ether sulfate having a pH of 3.5 was operated at a temperature of 15 to 30 C. over a current density range of 0.5 to 5 a./dm. to obtain lustrous, ductile zinc coatings with satisfactory covering power.

EXAMPLE VI An aqueous zinc bath containing 240 g./liter of crystalline zinc sulfate ZnSO -7H O, 30 g./liter of crystalline aluminum sulfate [Al (SO *18H O], 15 g./liter of sodium acetate, 1 g./liter of N-benzyl-N'-bis-('y-hydroxyethyl)thiourea and 5 g./liter of sodium lauryl ether sulfate having a pH of 4.0 was operated at a temperature of 15 to 30 C. over a current density range of 0.5 to 5 a./dm. to provide bright, ductile zinc coatings with satisfactory covering power.

EXAMPLE VII An aqueous zinc electroplating bath containing 110 gm./ liter of zinc chloride free from water of crystallization, 175 gm./liter of ammonium chloride, 0.5 gm./liter of N-phenyl-N'-('y-hydroxyethoxy-)-ethyl-thiourea, 0.2 gm./ liter of benzalacetone, and 5 gm./1iter of the adduct of 17 moles of ethylene oxide and 1 mole of isononyl alcohol having a pH of 4.6 was operated at temperatures of 15 to 30 C. over a current density range of 1 to 6 a./dm. to provide high-gloss, ductile zinc coatings with a good covering power.

EXAMPLE VIII An aqueous zinc electroplating bath containing 100 gm./liter of zinc chloride free from water of crystallization, 50 gm./ liter of crystalline aluminum chloride 150 gm./liter of ammonium chloride, 1 gm./liter of N- benzyl-N-(' -hydroxyethoxy-) ethyl-thiourea, 0.1 gm./ liter of acetophenone, and 6 gm./ liter of the adduct of moles of ethylene oxide and 1 mole of nonylphenol having a pH of 3.0 was operated at temperatures of 15 to 30 C. over a current density range of 1 to S a./dm. to provide bright, ductile zinc deposits with a good covering power.

EXAMPLE IX An aqueous zinc electroplating bath containing 400 gm./liter of crystalline zinc sulfate ZnSO -7H O, 15 gm./liter of ammonium chloride, 30 gm./liter of boric acid, 0.7 gm./liter of N-octy1-N'-( -hydroxyethoxyd ethyl-thiourea, 0.3 gm./ liter of the ethyl ester of benzoylacetic acid and 5 gm./ liter of a sodium salt of the C -C fatty alcohol sulfate mixture with a pH of 3.5 was operated at temperatures of 15 to 30 C. over a current density range of 0.5 to 3 a./dm. to provide bright, ductile Zinc deposits with a satisfactory covering capacity.

EXAMPLE X EXAMPLE XI An aqueous zinc electroplating bath containing 240 gm./ liter of crystalline zinc sulfate ZnSO -7H O, 30 gm./

liter of crystalline aluminum sulfate Al (S0' -18H O, 15 gm./liter of sodium acetate, 1 gm./liter of N-bis-(B- hydroxyethyl)-amino-N-phenyl-thiourea, 1 gm./liter of benzal-acetone, and 5 gm./liter of a sodium salt of the adduct of C1ZC14 fatty alcohol sulfate with 2 moles of ethylene oxide with a pH of 4.0 was operated at temperatures of 15 to 30 C. over a current density range of 1 to 5 a./dm. to provide high-gloss ductile zinc deposits with a satisfactory covering capacity.

Various modifications of the bath and process of the invention may be made without departing from the spirit or scope thereof and it should be understood that the invention is to be limited only as defined in the appended claims.

We claim:

1. In an acid aqueous electroplating bath for forming lustrous zinc deposits comprising a bath containing a water-soluble zinc salt, usual lustering agents and wet ting agents, optionally an additional conducting salt, a thiourea derivative of the formula wherein R is selected from the group consisting of alkyl of 6 to 22 carbon atoms, a monoor polynuclear aryl which may optionally be substituted with an aliphatic or aromatic group, arylalkyl and cycloalkyl, R is selected from the group consisting of hydrogen and hydroxyalkyl of 2 to 6 carbon atoms which may optionally be interrupted by an ether oxygen and R is hydroxyalkyl of 2 to 6 carbon atoms which may be optionally interrupted by an ether oxygen, the improvement comprising incorporating in the bath from 0.01 to 10 gm. per liter of bath liquid of an aromatic carbonyl compound selected from the group consisting of wherein R is aryl, A is selected from the group consisting of saturated alkylene with 1 to 7 carbon atoms and unsaturated alkylene with 2 to 7 carbon atoms and R is lower alkyl with 1 to 7 canbon atoms optionally substituted with a member selected from the group consisting of keto, carboxy, and carbal'koxy of 1 to 7 carbon atoms.

2. The bath of claim 1 containing 0.01 to 10 gm. per liter of bath liquid of the thiourea derivative.

3. The bath of claim 2 wherein the amount of thiourea is 0.1 to 5 gm. per liter.

4. The bath of claim 1 wherein the zinc salt is zinc chloride and the bath further contains a wetting agent selected from the group consisting of adducts of ethylene oxide with an alkyl phenol and adducts of ethylene oxide with aliphatic alcohol of 8 to 22 carbon atoms.

5. The bath of claim 4 wherein the number of moles of ethylene oxide is 2 to moles per mole of hydroxyl compound.

6. The bath of claim' 1 wherein the zinc salt is zinc sulfate and the bath further contains a wetting agent selected from the group consisting of fatty alcohol sulfates, fatty alcohol ether sulfates and polyalkylene glycols.

7. The bath of claim 6 wherein the wetting agent is selected from the group consisting of sulfates of fatty alcohols of 8 to 18 carbon atoms, ether sulfates of fatty alcohols of 8 to 18 carbon atoms and polyethylene glycols and polypropylene glycols with a molecular weight of 200 to 600.

8. The bath of claim 1 containing 0.5 to 10 gm. per liter of bath liquid of a wetting agent.

9. The bath of claim 1 wherein the concentration of the aromatic carbonyl compound is from 0.01 to 5 gm. per

liter of bath liquid.

7 8 10. The bath of claim 1 wherein the aromatic carbonyl References Cited compound has the formula STATES P 3 3,694,330 9/1972 Korpium et a1. 20455 R Ra -R4 5 3,700,570 10/1972 Hartenstein 20'455 R wherein A is vinylene and R is phenyl. FOREIGN PATENTS 11. A method of forming lustrous zinc deposits which comprises passing an electric current at a current density 1171 11/1967 Great Bmam 204-755 R of 0.5 to 8.0 a./dm. through an electroplating bath of claim 1 operating at a temperature of 10 to 40 C. 1 FREDERICK EDMUNDSON Pnmairy Exammer 12. The method of claim 11 wherein the pH of the Us CL XR. bath is 3 t0 5. 204 i 2 13. The method of claim 11 wherein the operating temperature is 15 to 30 C. 

